Re: [PATCH tip 1/1] perf_counter tools: Add locking to perf top

[Peter Zijlstra <a.p.zijlstra@chello.nl>]

On Fri, 2009-05-29 at 17:03 -0300, Arnaldo Carvalho de Melo wrote:
>         /* Sort the active symbols */
> -       list_for_each_entry_safe(syme, n, &active_symbols, node) {
> -               if (syme->count[0] != 0) {
> +       pthread_mutex_lock(&active_symbols_lock);
> +       syme = list_entry(active_symbols.next, struct sym_entry, node);
> +       pthread_mutex_unlock(&active_symbols_lock);
> +
> +       list_for_each_entry_safe_from(syme, n, &active_symbols, node) {
> +               syme->snap_count = syme->count[0];
> +               if (syme->snap_count != 0) {
> +                       syme->weight = sym_weight(syme);

That looks wrong, you basically do a fancy cast while holding the lock,
then you overwrite the variable doing a list iteration without holding
the lock.

If list_add and list_del are under a lock, the iteration should be too.